Most people hate most surprises most of the time. It’s only when you secretly suspect that there’s going to be a surprise, and the surprise will be exactly what you wanted but didn’t have to ask for, or what you would have wanted if you had known that it was a possibility, that a “surprise” is enjoyable.

The only reason a plot twist works is that you’ve managed to convince people ahead of time that they won’t hate it.

Foreshadowing is hinting at an upcoming plot twist.

Using repetitive elements that stick out somehow is hinting at an upcoming plot twist (the blood-red items in The Sixth Sense, for example.)

One of the characters explaining exactly what’s going on is hinting at a plot twist (see: any mystery ever, where one character says, “Well, clearly what’s going on is X.” Oh boy).

Saying that there’s a plan and explaining the details is hinting at an upcoming plot twist. Watch the last line in a scene/chapter; writers do a LOT of this.

Small things starting to go wrong or just plain weird for the character is hinting at an upcoming plot twist of epic proportions.

A sudden raise in stakes–no matter how subtle–is hinting at an upcoming plot twist.

Nothing big having happened lately is hinting at an upcoming plot twist, although it’s not a guarantee that you won’t have a second, even bigger one right after the first.

The plot twist happens…and then you interrupt the action to establish just exactly what happened.

After the plot twist, people stand around and talk about that shocking plot twist.

At the end of the story, the characters are still talking about the plot twist.

The other side of this is that you can’t wink too broadly at the upcoming surprise. You have to rub your eye and say there’s dust in it or that your contacts are dry, as it were.

The perfect surprise is when the recipient can smugly say, “I knew it all along,” but not feel the humiliation of having to be actually told.